I purchased Ceriths, Nassarius, Astrea from Reeftopia. Pretty good prices and nice size critters. Free shipping minimum is somewhat reasonable also.
I bought the Star Astreas at $2.50 each as I read they can right themsleves if they fall over unlike the other astreas. I just ain't true. They can't turn themselves back over either and the cost at least twice the price! (But they are kinda cool)